Earthquakes II: Strain and Faults

Faults

• faults: a large brittle fracture in a rock body
• the point of origin for most earthquakes

Terminology

• movement range along a break in a rock body is fractions of an inch to miles
  • fractures: fractions of inches to inch movements
  • faults: feet to mile movements
• plate boundaries: contacts between tectonic plates

Normal Fault

• blocks move away from each other
• hanging wall block moves down relative to foot wall

Reverse (or Thrust) Fault

• blocks move towards each other
• hanging wall block moves up relative to foot wall

Strike-Slip Fault

• motion is lateral (like traffic driving)
• fault itself is vertical (no hanging wall or foot wall blocks)

Types of Strike-Slip Faults

• left-lateral: movement relatively to the left
• right-lateral: movement relatively to right